8 4 



VICTOR E. SHELFORD. 



spinea Hentz builds its web 1-3 ft. above the ground while 

 Acrosoma gracile Wai. builds 4-6 ft. above the ground (see 



Dahl, '08). 



TABLE V. 



EVAPORATION FROM POROUS CUP EVAPORIMETERS IN DIFFERENT STRATA OF 

 A SUMMER DRY MARSH, CAMBRIDGESHIRE, ENGLAND, DURING THREE 

 PERIODS BETWEEN JULY 9 AND SEPTEMBER 8, 1907. 

 (Yapp, '09, p. 299 and 294.) 



The above table shows marked differences in the rate of 

 evaporation, considerable differences in temperature at the 

 different levels and both due largely to vegetation. Differences 

 in light are also to be expected. Sherff ('12, p. 420) has found 

 conditions similar to the above by a two months' study of 

 evaporation on Skokie marsh near Chicago. The evaporation 

 there was three times as great at a height of 1.95 m. as at the 

 surface of the soil in among the plants of Phragmites. Mr. 

 Harvey has also secured similar (unpublished) results on the 

 prairie at Chicago Lawn, Chicago. 



It has been long recognized that there are distinct growth- 

 form strata in nearly all plant formations, pelagic algse forma- 

 tions being a possible exception. The data of Sherff and Yapp 

 indicate differences in conditions in the strata of grass formations 

 and associations. Greater differences are to be expected in the 

 different strata of forests and shrub covered areas. Mr. Fuller 

 informs us that there are marked differences in the structure of 

 leaves at different levels of the same forest tree. 



6. Apparent Anomalous Distribution. 



Are physical conditions sometimes similar when vegetation 

 and landscape aspect are very different? That they are is 



